Hybrid 3d printing with photo-curable materials

ABSTRACT

A method of 3D printing comprises extruding one or more photo-curable materials from a nozzle to form a first layer that has a first shape specified by the one or more digital files, wherein the first shape corresponds to a first minimum line width that is based on, and narrower than, a diameter of the nozzle. The method further includes directing a light beam onto the first layer according to the one or more digital files to cure a portion of the first layer to create a first cured layer, wherein the first cured layer corresponds to a second shape of a first layer of a 3D printed orthodontic aligner, wherein the light beam has a beam diameter that is smaller than the diameter of the nozzle, and wherein the second shape has a second minimum line width that is smaller than the first minimum line width.

RELATED APPLICATIONS

This patent application is a continuation application of U.S.application Ser. No. 17/689,854, filed Mar. 8, 2022, which is acontinuation application of U.S. application Ser. No. 16/571,029, filedSep. 13, 2019, which claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Application No. 62/731,610, filed Sep. 14, 2018, both ofwhich are herein incorporated by reference.

TECHNICAL FIELD

The technical field relates to three-dimensional (3D) printing and, inparticular, to a hybrid 3D printing technique that uses resindispensing/extrusion of potentially photo-curable materials and one ormore light sources to generate objects with high spatial resolutionand/or potentially without support structures.

BACKGROUND

There are multiple types of three-dimensional (3D) printers thatfabricate 3D objects through an additive process. Different types of 3Dprinters can perform different 3D printing techniques, which may in turndepend on different applications. Each type of 3D printing technique mayhave advantages and disadvantages compared to others.

One example of a 3D printing technique is stereolithography (SLA), alsoknown as optical fabrication solid imaging. In SLA, an object isfabricated by successively printing thin layers of a photo-curablematerial (e.g., a polymeric resin) on top of one another. For right-sideup (also known as top-down) SLA, a platform rests in a bath of a liquidphotopolymer (e.g., resin) just below a surface of the bath. A lightsource (e.g., an ultraviolet laser) traces a pattern over the platform,curing the photopolymer where the light source is directed, to form alayer of an object. The platform is then lowered incrementally, and thelight source traces a new pattern over the platform to form anotherlayer of the object at each increment. This process repeats until theobject is fabricated. In inverted SLA (upside-down or bottom-up SLA), aportion of a platform begins within a shallow bath of a liquidphotopolymer or resin just below a surface of the bath. A light source(e.g., an ultraviolet laser) traces a pattern over the platform from thebottom through a transparent bottom with a non-stick surface, curing thephotopolymer where the light source is directed, to form a layer of anobject. The platform is raised incrementally, and the light sourcetraces a new pattern over the platform to form another layer of theobject at each increment. This process repeats until the object isfabricated.

Another 3D printing technique is digital light processing (DLP). DLPfunctions in much the same manner as SLA, except that with SLA the lightsource is generally a laser and with DLP the light source is a DLPprojector.

SLA and DLP have high accuracy, and are able to produce objects withfine details. SLA and DLP work with photo-curable materials that have upto a certain viscosity. However, photo-curable materials that have aviscosity that is higher than the maximum viscosity for SLA and DLPcannot be used effectively with SLA or DLP 3D printers. For example, ifthe viscosity is high (e.g., if the photo-curable material is tooviscous), then the uncured material will not fill in over the platform,or will do so too slowly to be commercially viable. For example, resinsof low viscosity, e.g., generally about 20-40 mPa-s, are used for SLAand DLP processes.

Additionally, both right-side up SLA and DLP and inverted SLA and DLPsystems require the use of support structures for most parts, dependingon their design. In right-side up systems, these supports hold parts ata precise location to ensure that all details have something to attachto, and resist lateral pressure from the resin-filled blade. Invertedstereolithography uses supports to attach overhanging parts to the buildplatform, prevent deflection due to gravity, and retain newly createdsections during the peel process. After the object is completed usingSLA or DLP, the support structures need to be removed, and the areas atwhich the support structures were previously located are polished.Regardless of orientation, supports are generally needed to startprinting a part and to support any overhanging features. For someobjects with complex geometries it can be difficult or impossible tocompletely remove support structures generated during the SLA or DLPprocess. This can render such objects unusable for their intendedpurpose in some situations.

As discussed above, many SLA and DLP techniques are very accurate andthat result in fine details. However, SLA and DLP do not workeffectively with photo-curable materials that exceed variousviscosities. For example, SLA and DLP are generally used withphoto-curable materials having viscosities of around 0.35-1.0 Pascalsecond (Pa-s) at 30° C. (e.g., around 20-40 mPa-s) at processingtemperatures. The photo-curable materials used for SLA and DLP aregenerally composed of carbon chains. The shorter the carbon chain, theless viscous the photo-curable material and the weaker the mechanicalproperties of the ultimate 3D object manufactured by the SLA or DLPprocess. Photo-curable materials that have strong mechanical propertiesoften have a viscosity that is too high for use with SLA or DLP (e.g.,around 10-100 Pa-s or greater at 30° C.). Some objects (such asorthodontic aligners) may function better if they are manufactured fromphoto-curable materials with strong mechanical properties. However,dental appliances that have sufficient mechanical properties forclinical use (e.g., to correct malocclusion) have thus far not beenmanufacturable using SLA or DLP in a manufacturing environment at leastin part because printing of such parts using materials exceeding certainviscosities is too slow and/or is not possible. Some of this has beenovercome by increasing the temperature of the resin and the vat of resinto decrease its viscosity at the elevated printing temperature. But,this this tends to decrease the pot life of the vat of resin.

Another 3D printing technique is fused deposition modeling (FDM).Traditional FDM printers melt a string of thermoplastic filament and laythe melted string down onto a print bed in a layer-by-layer manner inorder to form a 3D object. FDM is a low cost type of 3D printingtechnique. However, FDM has low accuracy and produces objects that lackfine details.

FDM is often fast, but quite often has low accuracy and cannot producefine details (e.g., has low clarity and feature resolution).Additionally, the thermoplastics that are used for FDM 3D printing mayhave mechanical properties that render them unsuitable for certain typesof objects such as dental appliances including orthodontic aligners.Accordingly, dental appliances, e.g., orthodontic aligners, that havesufficient mechanical properties for clinical use have also thus far notbeen manufacturable using FDM.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings, inaccordance with some embodiments.

FIG. 1 illustrates an example of a three-dimensional (3D) printed objectwith support structures.

FIG. 2 illustrates a hybrid 3D printer, in accordance with someembodiments.

FIG. 3A illustrates a top-down view of a cross section of a printedlayer that has been printed using a hybrid 3D printer, in accordancewith some embodiments.

FIG. 3B illustrates another top-down view of a cross section of aprinted layer that has been printed using a hybrid 3D printer, inaccordance with some embodiments.

FIG. 4 illustrates a flow diagram for a method of performing 3Dprinting, in accordance with some embodiments.

FIG. 5 illustrates a block diagram of an example computing device, inaccordance with some embodiments.

DETAILED DESCRIPTION

The embodiments herein relate to methods of three-dimensional (3D)printing, devices used to form objects using methods of 3D printing, andsystems incorporating the same. As noted herein, the techniques hereinmay be used to print various objects. The implementations describedherein specify one or more hybrid 3D printing techniques to 3D print anobject. Various implementations may include placing a first materialthat is to form the basis of walls of a vat, and dispensing one or moresecond materials (e.g., one or more resins and/or photo-curablematerials)) within the walls created by the first material. A“photo-curable material,” as used herein, may include a material thatchanges its properties when exposed to radiation, such as light (e.g.,light in the ultraviolet or visible regions of the electromagneticspectrum). These changes may be manifested structurally, for examplehardening of the material occurs as a result of cross-linking whenexposed to light. A “vat,” as used herein, may refer to a formedstructure comprising printed walls that define a reservoir configured tocontain the one or more second materials.

The one or more second materials may be placed through extrusion orother dispensers. The one or more second materials may be selectivelycured portions in a spatially controlled manner. Curing may involveapplication of light (or other curing radiation) and/or reactive mixingof the resin with one or more other materials. Spatial control of curingmay involve limiting application of the curing to form patterns,designs, shapes, etc. to the one or more second materials so that onlyportions of the one or more second materials are cured. The spatialcontrol may be based on patterns, designs, shapes, etc. derived from adigital file used to define properties of layers of the object to be 3Dprinted. The operations of placement of the first material, placement ofthe one or more second materials, and selective curing in a spatiallycontrolled manner may be repeated layer-by-layer until the object isformed.

The hybrid 3D printing techniques described herein may provide similaraccuracy and/or resolution (e.g., minimum line width) of SLA and DLPtechniques. Additionally, the hybrid 3D printing techniques described inembodiments may provide printing speeds comparable to the printing speedof FDM. In contrast to SLA, DLP and FDM, the hybrid 3D printingtechniques described herein may be usable with viscous photo-curablematerials (which cannot practicably be used with existing SLA and DLPsystems) that are used to form various objects, such as a dentalappliance (e.g., a directly fabricated (e.g., 3D printed) dentalappliance (e.g., removable aligners (e.g., removable orthodonticaligners) used to implement a treatment plan, dental attachmentplacement templates, retainers, incremental and/or hybrid palatalexpanders, etc.), a mold used to form a dental appliance, etc.

In some embodiments, the techniques herein can be used to form molds,such as thermoforming molds. Examples of these can be found in: U.S.Pat. No. 9,943,991, by inventors Tanugula et al., entitled “Mold withseparable features;” U.S. Pat. No. 9,943,386, to inventors Webber etal., entitled “Mold with weakened areas;” and U.S. Pat. No. 8,776,391 toinventors Kaza et al., entitled “System for post-processing orthodonticappliance molds;” as well as any continuation or divisional applicationclaiming priority and any utility or provisional application to whichthese claim priority therefrom. These patents/applications are herebyincorporated by reference as if set forth fully herein.

In some embodiments, the techniques herein can be used to formappliances with mandibular repositioning features. Examples of these canbe found in: U.S. Pat. No. 9,844,424 by inventors Wu et al., entitled,“Dental appliance with repositioning jaw elements;” U.S. Pat. Pub. No.2015/0238280 by inventors Wu et al., entitled “Dental appliance withrepositioning jaw elements;” U.S. Pat. No. 10,213,277 by inventorsWebber et al., entitled “Dental appliance binding structure;” as well asany continuation or divisional application claiming priority and anyutility or provisional application to which these claim prioritytherefrom. These patents/applications are hereby incorporated byreference as if set forth fully herein.

In some embodiments, the techniques herein can be used to form palatalexpanders. Examples can be found in: U.S. Pat. No. 9,610,141 byinventors Kopelman et al., entitled, “Arch expanding appliance;” U.S.Pat. No. 7,192,273 by inventor McSurdy entitled “System and method forpalatal expansion;” U.S. Pat. No. 7,874,836 by inventor McSurdy entitled“System and method for palatal expansion;” as well as any continuationor divisional application claiming priority and any utility orprovisional application to which these claim priority therefrom. Thesepatents/applications are hereby incorporated by reference as if setforth fully herein.

In some embodiments, the techniques herein can be used to formattachment formation templates. Examples can be found in: U.S. Pat. Pub.No. 2017/0007368 by inventor Boronkay entitled “Direct fabrication ofattachment templates with adhesive;” U.S. Pat. Pub. No. 2017/0165032 byinventors Webber et al., entitled “Dental attachment placementstructure;” U.S. Pat. Pub. No. 2017/0319296 by inventors Webber et al.,entitled “Dental attachment placement structure;” the contents of U.S.patent application Ser. No. 16/366,686 by inventors Webber et al.,entitled “Dental attachment placement structure;” as well as anycontinuation or divisional application claiming priority and any utilityor provisional application to which these claim priority therefrom.These patents/applications are hereby incorporated by reference as ifset forth fully herein.

In some embodiments, the techniques herein can be used to form directlyfabricated aligners. Examples can be found in: U.S. Pat. App. Pub. No.2016/0310236 by inventors Kopelman et al., entitled “Direct fabricationof orthodontic appliances with elastics;” U.S. Pat. App. Pub. No.2017/0007365 to Kopelman et al., entitled “Direct fabrication ofaligners with interproximal force coupling;” U.S. Pat. App. Pub. No.2017/0007359 to Kopelman et al., entitled “Direct fabrication oforthodontic appliances with variable properties;” U.S. Pat. App. Pub.No. 2017/0007360 to Kopelman et al., entitled “Systems, apparatuses andmethods for dental appliances with integrally formed features;” U.S.Pat. No. 10,363,116 to Boronkay entitled “Direct fabrication of powerarms;” U.S. Pat. App. Pub. No. 2017/0007366 to Kopeleman et al.,entitled “Direct fabrication of aligners for arch expansion;” U.S. Pat.App. Pub. No. 2017/0007367 to Li et al., entitled “Direct fabrication ofpalate expansion and other application;” as well as any continuation ordivisional application claiming priority and any utility or provisionalapplication to which these claim priority therefrom. Thesepatents/applications are hereby incorporated by reference as if setforth fully herein.

Examples of materials that can be used with the embodiments discussedherein include the subject matter of U.S. Pat. Pub. No. 2017/0007362, byinventors Yan CHEN et al., entitled, “Dental Materials Using ThermosetPolymers;” International Patent Application Number PCT/US2019/030683 toALIGN TECHNOLOGY, INC., entitled “Curable Composition for Use in a HighTemperature Lithography-Based Photopolymerization Process and Method ofProducing Crosslinked Polymers Therefrom; and International PatentApplication Number PCT/US2019/030687 to ALIGN TECHNOLOGY, INC.,entitled, “Polymerizable Monomers and Method of Polymerizing the Same.”These patents/applications are hereby incorporated by reference as ifset forth fully herein. As noted herein, the hybrid 3D printingtechniques may combine advantages of SLA, DLP and FDM into a singletechnology that can be used as the basis of 3D printing objects (dentalappliances, hearing aids, medical implants, etc.) for mass production.

In some embodiments, example methods involve one or more of thefollowing operations: (1) Placing a first material that comprises (e.g.,forms the basis of) the walls of the vat. (2) If the first materialrequires photo-curing and/or other treatment, then performing thephoto-curing and/or other treatment. (3) Within the walls of the vat,dispensing one or more materials (e.g., one or more second materials)into the vat, for instance, within the walls formed by the firstmaterial. The one or more second materials may be cured by light and/orother mechanisms as needed for each material. In some embodiments, atleast one of the cure mechanisms is the use of light. In variousembodiments, the cure of the one or more materials may be controlled ina spatially resolved manner. Some embodiments may call for use of lasersand/or DLPs to spatially control the curing of the material. (4) If morethan one layer is to be made, then the vat wall may be increased inheight and the filling of the internal volume of the vat may beperformed again, followed by any needed curing of the one or morematerials in that layer. (5) As noted herein, in some embodiments, theprocess may be continued until a full object is printed with itsgeometry and/or other physical properties. (6) The object may then beremoved from the vat and processed by post printing cleaning procedures.

As noted herein, the use of a vat may be optional in some embodiments.For instance, in some embodiments, the vat is not needed (the viscosityof the resin may be high enough to prevent the resin from flowing on thetime scale that the printing process occurs, etc.). The resin materialmay be extruded/dispensed in layers using a Fused Deposition Modeling(FDM) process that include the use of light or other curing mechanism tocure all or part of the extruded resin.

In some embodiments, the vat is provided before the printing processbegins. This can be useful for objects that are not very tall in heightand/or have the same or approximately the same shape each print.

In some embodiments, the vat material is one of the materials used tomake the printed object.

In some embodiments, one or more of the materials are hot melt materialssuch as those typically used in FDM style 3D printing.

In some of the embodiments, one or more of the materials arethermosetting materials. Examples of thermosetting materials are furtherdiscussed herein.

In some embodiments, 2 or more materials are mixed during dispensingsuch as with a static mixer. Such materials may react with each other toform a new material. Some non-limiting examples of materials that can bemade and reactions that can be used are urethanes, amine-epoxies,Michael additions, Epoxies, Ring opening reactions/polymerizations,vulcanization, silane and siloxane materials, diel-alders reactions,ROMP reactions, etc. It is also possible to use the mixing of twomaterials during dispensing to incorporate either non reacting materialsor reactive materials such as pigments, dyes, flavors, fragrances,drugs, fillers, solvents, plasticizers, catalysts, initiators, etc.

In some embodiments, the material may be destroyed, trimmed, burned, orother otherwise removed within one or more layers such as by mechanicalmeans such as dremels, milling, sanding, gouging, die cutting, etc.and/or by optical means such as laser cutting and/or other ablationtechniques and/or physical techniques such as boiling, subliming, orsucking material.

In some embodiments, a material or object may be introduced by placingthe material into a cavity created by removing material from one or morelayers. Such introduced materials/objects may be place into a holecreated via subtractive mechanisms such as described above or may pushmaterial in the layer(s) out of the way (easiest if a liquid) or simplyplaced on top of the uppermost layer. Further layer creation can occuron top of and/or around the introduced material/object. Somenon-limiting example objects and/or materials are ECIs or otherelectronic devices, mechanical supports such as metal wires, or plasticsheets, fibers, glass, ceramics, metal sheets, sensors, indicators, etc.Pick and place technologies are useful for introducing various objectsinto the printed object during the printing process. Robotic arms ofvarious types can be designed to perform needed placement ofobjects/materials.

The device can use small needles or tubes for extruding/dispensingmaterial(s) onto the substrate or layer. Additionally, this device mayuse jetting technology such as Nordson EFD's PICO Pμlse and/or use ofmicro extrusion such as the TWW Micro Extruder and/or micro dispensingsystems such as Vermes Micro Dispensing System—MDS 3280. In general, thedevice is able to deliver high and/or low viscosity materials to theprint area. Additionally, the device has the option of having more thanone material delivery head and/or more than one delivery method. Allthese methods are scalable, and though they are currently listed in themicro liter range, higher and smaller scale dispensers could be useddepending on the needed resolution and desired speed of the finalprinted object.

Once material is delivered to the print area, some or all of it is curedin a spatially controlled manner such as by light and/or reactive mixingand dispensing. Each layer is created by delivering more material in acontrolled manner to the vat.

The laser and/or projection system are typically focused onto the upperlayer surface or just barely into the top layer surface. Addition oflayers requires that the focal points of the light source to beadjusted. The focal points of the light source can be controlled byoptically sensing the location of the surface (such as performed in anOctave 3D printer) or various forms of machine vision (to name twonon-limiting examples) and adjusting the optical system and/or the vatheight to keep the focus in the right location. Another potential methodis to adjust the vat height based on the amount of material dispensed.The light source can be adjusted or the height of the vat can beadjusted to account for the height of the new layer by calculationsbased on the known or measured or calculated volume of the vat and theamount of material delivered (devices or sensors to measure the amountof material delivered is useful for this embodiment). Mechanical floats,hall sensors, temperature sensors, and other mechanical and electricalsensors can also be used to determine the location of the surface of thelayer. Optical methods are most preferred. The process of addingmaterial to the print area and curing is repeated until a printed objectis complete.

Pick and place operations can occur at any stage of the print processand may include removing objects.

One feature is the ability to quickly deliver large amounts of one ormore materials to the print area in time frames that make the wholeprocess of printing a well resolved object possible in a reasonable timeframe such that mass manufacturing can be cost effective. Currently, inkjets can make multi material objects similar to the device describedherein, but the time required to print is very long. SLA and DLPprinters are not effective at printing multi materials objects, unlikethe embodiments described herein. Time frames that are useful forprinting aligners and/or medical devices in a manufacturing or doctor'soffice environments are 10 seconds to 1 min per device, 1 min to 5minutes per device, 5 minutes to 10 minutes per device, 10 to 30 minutesper device, 30 minutes to 2 hours per device, and 2 hours to 6 hours perdevice. Shorter times are generally more desirable.

In some embodiments, the material is heated prior and/or duringdispensing to facilitate flow of the material out of the dispenser. In afew embodiments, it is useful to cool a material before dispensing. Forexample, a super-cooled solution (such as water as an example) can bedispensed from the head at which time it instantly freezes. This can beused as vat materials or supports in some embodiments.

Resolution

The resolution of the final part is controlled by the size of thedelivery method and the resolution of the curing mechanism. In one mainembodiment, the material is delivered in microliter (or pico liter)quantities and cured using a light source such a DLP. Typicalresolutions of DLP are 30×30 microns in the x/y plane up to 100×100microns. Other ranges are also possible depending on the needs requiredby the print. Lasers can provide focal points downs to 10 microns (orless), but typically range from 30 to 100 microns. Holographicprojectors such as those being created by Pacific Light and Hologram arealso useful in various embodiments as a curing source.

The z dimensional resolution may be controlled by the amount of lightabsorber in the resin when light curing is used. It may also becontrolled by the amount of resin delivered to the print area. Forinstance, once the vat wall is present, the volume of resin per layercan be calculated and accurately delivered. This can easily control thelayer height. Optionally, an optical or other sensing method (such asweight) can be used to determine the height of the layer in a feedbacksystem. It is expected that layer heights can range from 1 micron to 50microns and/or greater than 100 microns. Each layer height can becontrolled independently to other layers. Layer height is also afunction of the scale of the object to be printed combined with thedesired z dimensional resolution. Printing of large scale objects thatare 10s of centimeters in height may use a z dimensional layer spacingof 1 mm or even 1 cm. Such scaling options are anticipated.

Resolution of the composite material components of the printed object iseither controlled by x/y resolution of the curing mechanism and/or bythe z dimensional height control. This is true when each layer is adifferent material (for example is layer one if material A and layer 2is material B and subsequent layers alternate between A and B).

When each layer comprises more than one material, then the compositedimensions are controlled by the above factors in addition to where thespatial curing is taking place. For instance, if two or more dispensingheads are dispensing two different materials side by side and eachliquid is 100 microns wide, a cure system of 100 microns width cancreate a 50 micron wide material A connected to a 50 micron widematerial B. Alternatively, a cure system curing a 50 micron width linemight create two (or more) strips of 50 micron wide strips of material Aand Material B, which may not be connected together at that location.However, the two materials may be present in the same layer. Thus, theresolution of the materials that comprise the composite has multiplepossibilities when using the embodiments described herein.

In some embodiments that use multiple materials, the different materialsare fed through a series of channels or tubes into a single dispensingor extruding tube. In such an embodiment, the different materials aremetered or delivered into the single tube and dispensed as needed. Itmay be useful to purge any remaining material before delivering a newmaterial and such purging of material may be done outside the vat, intoa separate vat, or into areas within the vat that are not part of theobject being printed. Mixing of two or more materials may also be donewith such a set up and depending on the viscosities and flow propertiesof the materials and the channel diameters, laminar flow can prevent thematerials from mixing thus allowing the two or more materials to bedispensed as an unmixed combination of materials after which it can becured in that state and thus preserve the unmixed structure.

In some embodiments, the one or more dispensing heads are able todeliver material at the same time other heads are dispensing material.Such configurations allow for fast layer creation with one or morematerials in each layer.

In many embodiments, material placement is controlled by a computerwhich controls the heads such that material is placed in locations asdetermined by an input file and then a computer controls where thematerials are to be cured as determined by an input file.

Though the terms tubes and needles have been used to describe the outputfrom a dispensing head, other shapes are contemplated. Some non-limitingexamples are ribbons, rectangles, ovals, stars, or other shapes.

In embodiments that use a vat, the material delivery heads may need tobe retractable or height adjustable so as to be able to traverse overthe vat wall in order to dispense inside the vat. This is especiallytrue if there are more than 1 material delivery heads. This can also beaccomplished by moving the vat up and down, though this is lesspreferred. A computer can be used to determine the best way and/orheight of retraction of the print heads during printing in order toavoid hitting or contacting the vat.

Light Source

One or more lasers can be used to cure the resins that are supplied tothe print area. The lasers can be used in a scanning configuration,common in the SLA industry, and or in other configurations such asflash. Lasers can also be used to create interference patterns that maybe useful in certain applications. A DLP device can also be used as isstandard in the 3D printing industry. Other methods of curing such as Ebeam, x ray, other forms of radiation, multiphoton, and/or heat(infrared) can be used independently or combined with each other.Holographic projectors and/or laser interference are also useful in someembodiments described herein.

Vat Material Descriptions

The material used to make the vat can be comprised of thermosets and/orthermoplastic materials. They can be delivered by any of the listeddelivery methods and if curing is needed, any curing method can be used.

It is preferred that the material be thixotropic such that as thematerial is delivered it does not change its shape too much or flow away(or it needs to be cured before it can flow away).

The vat layer may be level with the fill level of the vat.Alternatively, in some embodiments, the vat is created one layer aheadof the fill level represented by the current layer of the printed objectin the vat.

In some embodiments, the hybrid 3D printing techniques described hereininclude heating a highly viscous photo-curable material to reduce thephoto-material's viscosity, and then extruding the photo-curablematerial from a nozzle to form layers of an object according to adigital file. A first layer of the object may have a first shapespecified by the digital file. The first shape may have a first minimumline width based on a diameter of the nozzle. The new hybrid 3D printingtechnique further includes directing a light beam onto the layers of theobject as they are deposited (or after they are deposited) according tothe digital file or an additional digital file to cure a portion of eachof the layers. The cured portion of the first layer may have a secondshape within the first shape. The light beam used to cure the portion ofthe layers may have a beam diameter that is smaller than the diameter ofthe nozzle. Accordingly, the light beam may be used to produce detailsthat are much finer than those that can be produced simply by extrudingmaterial from the nozzle. As such, the second shape may have a secondminimum line width that is smaller than the first minimum line width.Extrusion in this disclosure can encompass various material deliverymethods comprising jetting technology such as Nordson EFD's PICO Pμlseand/or use of micro extrusion such as the TWW Micro Extruder and/ormicro dispensing systems such as dispensers such as Vermes MicroDispensing System—MDS 3280. Larger or smaller formats that scaledepending on the needed resolution of the printed part are alsopossible.

Existing 3D printing technologies, including FDM, SLA and DLP, allutilize support structures to support 3D printed objects during theprinting process. FIG. 1 illustrates an example printed 3D object 100with support structures 105. Support structures 105 are undesirable, asthey ultimately will not be part of the object 100. However, suchsupport structures 105 generally need to be added during the printingprocess to ensure that the object has a desired shape. For SLA and DLP,for example, the support structures 105 may hold the object at a preciselocation to ensure that all details of the object have something toattach to and/or to resist lateral pressure from a resin-filled blade,may attach the overhanging object 100 to a platform, may preventdeflection due to gravity, and/or may retain newly created sectionsduring a peel process.

The hybrid 3D printing technique described in some embodiments uses aphoto-curable material that is highly viscous at room temperature. Forexample, in embodiments the photo-curable material may become solid ornearly solid at room temperature. Portions of the depositedphoto-curable material are exposed to a light beam with a narrowerdiameter than a diameter of the nozzle used to deposit the photo-curablematerial. This enables objects to be built without support structuresand/or with reduced support structures since the photo-cured sections ofthe printed 3D object are encapsulated and supported by the uncured butfrozen portions of the photo-curable material.

FIG. 2 illustrates a sectional view of a hybrid 3D printer 200, inaccordance with some embodiments. The hybrid 3D printer 200 may be usedwith photo-curable materials that, when cured, have desirable mechanicalproperties such as high tensile strength, high elongation at break, highelongation at yield, high modulus of elasticity, high flexural strength,high creep resistance, low stress at relaxation and/or high flexuralmodulus. The hybrid 3D printer 200 may also be used to manufactureobjects with complex geometries without the use of support structures orwith minimal use of support structures. The hybrid 3D printer 200 may beused, for example, to directly manufacture orthodontic aligners used tocorrect malocclusion and/or to construct other dental appliances. It canalso be used to print composite structures.

In some embodiments, the hybrid 3D printer 200 includes a chamber body250 that encloses an interior volume 245. The chamber body 250 may befabricated from aluminum, stainless steel, plastic, ceramic and/or othersuitable material. The chamber body 250 generally includes sidewalls 255and a bottom 260. In alternative embodiments, the chamber body 250 maybe omitted.

Enclosed within the interior volume 245 of the chamber body 250 is aplatform (also known as a print bed) 205 to support a printed object222. The platform 205 may include a stepper motor that can move theplatform 205 along a vertical guideway (e.g., a set of vertical guiderods) 210 in the z direction according to instructions from acontroller. Alternatively, the stepper motor may be separated from theplatform 205, but may still drive the platform 205 along the verticalguideway 210.

Also enclosed within the interior volume 245 of the chamber body 250 isa guideway 220 onto which a dispenser (also known as an extruder) 215 ismounted. The dispenser 215 may include one or more stepper motors thatcan move the dispenser 215 along the guideway 220 and precisely controlthe position of the dispenser 215 in the xy plane. Alternatively, thestepper motor(s) may be separated from the dispenser 215, but may stillmove the dispenser 215 in at least the xy plane.

In some embodiments, the dispenser 215 is mounted to a mechanical stagethat is movable in at least the xy plane. In such embodiments, the oneor more stepper motors may be included in the mechanical stage. In someembodiments, a light source that emits a light beam that is usable tocure the photo-curable material is also mounted to the mechanical stage.For example, the dispenser 215 may be mounted to the mechanical stage ata first position and the light source may be mounted to the mechanicalstage at a second position. The light source mounted to the mechanicalstage may be rotatable or otherwise movable to direct the light beam toa target location regardless of a position of the mechanical stagewithin the interior volume 245 in embodiments.

In some embodiments, the dispenser 215 (and/or mechanical stage) is alsomovable along the z-axis. For example, in the illustrated embodiment thedispenser 215 moves in the xy plane and the platform 205 moves along thez axis (which may be the axis that is normal to a plane defined by theplatform). However, in some embodiments the platform 205 may bestationary and the dispenser 215 may be movable along the x-axis, they-axis and the z-axis.

The dispenser 215 may include a container that holds a viscousphoto-curable material. The dispenser 215 may additionally include oneor more heating element to heat at least a portion of the viscousphoto-curable material, a nozzle 218 to extrude the heated photo-curablematerial, and/or a feeder to feed the heated photo-curable through thenozzle 218. The feeder may be a pump, a piston, a screw mechanism, orother mechanism that applies a force to extrude the heated photo-curablematerial through the nozzle 218.

Though only a single dispenser 215 is shown, in embodiments the 3Dprinter 200 may include multiple dispensers (e.g., two or moredispensers), each of which may be moved independently and which mayoperate in parallel to speed up the deposition of the photo-curablematerial onto the platform 205. Additionally, more than onephoto-curable material may be provided by one or more dispensers.

The photo-curable material provides for a relatively high glasstransition temperature and a decreased rigidity and increased toughnessof polymerizates, i.e. high values of tensile modulus, tensile strengthat yield, elongation at break and stress relaxation in embodiments.

The photo-curable material may include materials such as a polyester, aco-polyester, a polycarbonate, a polypropylene, a polyethylene, apolypropylene and polyethylene copolymer, a polyurethane, an acrylic, acyclic block copolymer, a polyetheretherketone, a polyamide, apolyethylene terephthalate, a polybutylene terephthalate, apolyetherimide, a polyethersulfone, a polytrimethylene terephthalate, astyrenic block copolymer (SBC), a silicone rubber, an elastomeric alloy,a thermoplastic elastomer (TPE), a thermoplastic vulcanizate (TPV)elastomer, a polyurethane elastomer, a block copolymer elastomer, apolyolefin blend elastomer, a thermoplastic co-polyester elastomer, athermoplastic polyamide elastomer, a dendritic acrylate, a polyesterurethane acrylate, a multifunctional acrylate, a polybutadiene urethaneacrylate, a polyester urethane methacrylate, an aliphatic polyesterurethane methacrylate (e.g., such as a BOMAR XR-741 MS), an aliphaticdifunctional acrylate (e.g., such as Miramer UA5216), a polyetheracrylate, an acrylic polyester acrylate, a polyester acrylate, anacrylic acrylate, a polyether urethane methacrylate, a silicone urethaneacrylate, or combinations thereof. The photo-curable material mayadditionally include other materials in addition to, or instead of, theabove mentioned materials. The photo-curable material can be provided inan uncured form (e.g., as a liquid, resin, etc.) and can be cured (e.g.,by photopolymerization, light curing, laser curing, crosslinking, etc.).The properties of the material before curing may differ from theproperties of the material after curing. Once cured, the materialsherein can exhibit sufficient strength, stiffness, durability,biocompatibility, etc. for use in an aligner. The post-curing propertiesof the materials used can be selected according to the desiredproperties for the 3D printed object.

The photo-curable material may be a highly viscous resin formulationthat includes one or more components. The components may include one ormore polymerizable species (such as those mentioned above), one or morepolymerizable monomers that may be used as reactive diluents,polymerization initiators, polymerization inhibitors, solvents, fillers,antioxidants, pigments, colorants, surface modifiers, glass transitiontemperature modifiers, toughness modifiers, and/or mixtures thereof. Inorder for the photo-curable material to ultimately produce a curedpolymer (e.g., a cross-linked polymer) with sufficient mechanicalproperties to use for applications such as orthodontic aligners, thephoto-curable material may include long chain monomers. The inclusion ofsuch long chain monomers in the photo-curable material results in a highviscosity (e.g., such as a material that behaves as a solid at roomtemperature).

In some embodiments, polymerizable monomers included in thephoto-curable material as a reactive diluent may have low melting points(e.g., of less than 90° C., less than 50° C., or even less than 30° C.,which would result in the polymerizable monomer being liquid at roomtemperature) and substantially low volatility (e.g., a mass loss of <1wt % at temperatures of up to 90-120° C.). In some embodiments, thepolymerizable monomers are selected from the group consisting of thefollowing compounds:

-   2-isopropyl-5-methylcyclohexyl 2-(methacryloxy)benzoate (1);-   3,3,5-trimethylcyclohexyl 2-(methacryloxy)benzoate (2);-   1,3,3-trimethyl-2-bicyclo[2.2.1]heptanyl 2-(methacryloxy)benzoate    (3);-   1,7,7-trimethyl-2-bicyclo[2.2.1]heptanyl 2-(methacryloxy)benzoate    (4);-   3,3,5-trimethylcyclohexyl 3-(methacryloxy)benzoate (5);-   3,3,5-trimethylcyclohexyl 4-(methacryloxy)benzoate (6); and-   3,3,5-trimethylcyclohexyl 2-(acryloxy)benzoate (7).

Other possible reactive diluents that may be used include acrylates andmethacrylates such as such as (poly)glycol di(meth)acrylates, e.g. tri-or tetraethylene glycol dimethacrylate (TEGDMA), bisphenol Adimethacrylate or the hydrogenated form thereof,4,4′-isopropylidenedicyclohexanol di methacrylate, or salicylic ester(meth)acrylates; (poly)vinyl monomers, e.g. vinyl acetate, styrene,divinylbenzene. Some examples diluents are TEGDMA and salicylic ester(meth)acrylates such as cycloalkyl salicylate (meth)acrylates.

The photo-curable material extruded by the dispenser 215 may be a highlyviscous resin. The photo-curable material may have a viscosity ofgreater than 100 Poiseuille (Pa-s) (e.g., a viscosity of 300 Pa-s ormore) at room temperature and a viscosity of below 70 Pa-s (e.g., 0.3Pa-s, 1 Pa-s, 5 Pa-s, 10 Pa-s, 20 Pa-s, 30 Pa-s, 40 Pa-s, 50 Pa-s, 60Pa-s, etc.) at processing temperatures at or above 50° C. (e.g. in therange from 90° C. to 130° C.) in some embodiments. In furtherembodiments, the photo-curable material may have a viscosity of under 2Pa-s (e.g., around 1-2 Pa-s) at the processing temperatures and may havea viscosity of over 10 Pa-s (e.g., around 10-300 Pa-s) at roomtemperature. The dynamic viscosity of a fluid indicates its resistanceto shearing flows. The SI unit for dynamic viscosity is the Poiseuille(Pa-s). Dynamic viscosity is commonly given in units of centipoise,where 1 centipoise (cP) is equivalent to 1 mPa-s. In some embodiments,the photo-curable material has a viscosity as set forth in the belowtable. The presence of the reactive diluent(s) (e.g., the polymerizablemonomers) may provide for a viscosity of the photo-curable material ofless than 70 Pa-s at the processing temperatures, even though thecomposition (without the reactive diluent(s)) may have a viscosity ashigh as 300 Pa-s or more, or may even be solid, at room temperature insome embodiments.

TABLE 1 Viscosities at varying temperatures Example n at 25° C. n at 50°C. n at 70° C. n at 90° C. Resin [Pa-s] [Pa-s] [Pa-s] [Pa-s] BOMAR 1,25016.2 1.6 0.3 XR-741 MS + polymerizable monomer Miramer 734 78.7 20.0 6.7UA5216 + polymerizable monomer

In some embodiments, the photo-curable material including one or morepolymerizable species and at least one photopolymerization initiator maybe heated to an elevated process temperature (e.g., 60-130° C., 90-120°C., etc.) before becoming irradiated with light of a suitable wavelength(e.g., UV light) to be absorbed by said photoinitiator, thereby causinga cleavage of the photoinitiator to induce polymerization of the one ormore polymerizable species to obtain a crosslinked polymer. If thephoto-curable material includes one or more polymerizable monomers, thepolymerizable monomers may become co-polymerized in the polymerizationprocess, resulting in an optionally crosslinked polymer comprisingmoieties of the polymerizable monomer as repeating units.

As used herein, the term “polymer” refers to a molecule composed ofrepeating structural units connected by covalent chemical bonds andcharacterized by a substantial number of repeating units (e.g., equal toor greater than 10 repeating units and often equal to or greater than 50repeating units and often equal to or greater than 100 repeating units)and a high molecular weight (e.g. greater than or equal to 5,000 Da,10,000 Da or 20,000 Da). Polymers are commonly the polymerizationproduct of one or more monomer precursors. The term polymer includeshomopolymers, or polymers consisting essentially of a single repeatingmonomer subunit. The term polymer also includes copolymers which areformed when two or more different types of monomers are linked in thesame polymer. Copolymers may comprise two or more monomer subunits, andinclude random, block, alternating, segmented, grafted, tapered andother copolymers. “Crosslinked polymers” refers to polymers having oneor multiple links between at least two polymer chains, which may resultfrom multivalent monomers forming crosslinking sites uponpolymerization.

Photopolymerization occurs when suitable formulations are exposed tolight of sufficient power and of a wavelength capable of initiatingpolymerization. The wavelengths and power of light useful to initiatepolymerization of the photo-curable material depends on the initiatorused. Light as used herein includes any wavelength and power capable ofinitiating polymerization. Preferred wavelengths of light includeultraviolet (UV) or visible. UV light sources include UVA (wavelengthabout 400 nm to about 320 nm), UVB (about 320 nm to about 290 nm) or UVC(about 290 nm to about 100 nm). Any suitable light source may be used,including laser sources. The light source may be broadband ornarrowband, or a combination thereof. The light source may providecontinuous or pulsed light. Both the length of time the system isexposed to UV light and the intensity of the UV light can be varied todetermine the ideal reaction conditions.

In some embodiments, the materials that comprise the final printedobject are biocompatible and bioinert materials. “Biocompatible,” asused herein, may refer to a material that does not elicit animmunological rejection or detrimental effect, referred herein as anadverse immune response, when it is disposed within an in-vivobiological environment. For example, in embodiments a biological markerindicative of an immune response changes less than 10%, or less than20%, or less than 25%, or less than 40%, or less than 50% from abaseline value when a human or animal is exposed to or in contact withthe biocompatible material. Alternatively, immune response may bedetermined histologically, wherein localized immune response is assessedby visually assessing markers, including immune cells or markers thatare involved in the immune response pathway, in and adjacent to thematerial. In an aspect, a biocompatible material or device does notobservably change immune response as determined histologically. In someembodiments, the photo-curable material is used to manufacturebiocompatible devices configured for long-term use, such as on the orderof weeks to months, without invoking an adverse immune response.Biological effects may be initially evaluated by measurement ofcytotoxicity, sensitization, irritation and intracutaneous reactivity,acute systemic toxicity, pyrogenicity, subacute/subchronic toxicityand/or implantation. Biological tests for supplemental evaluationinclude testing for chronic toxicity.

“Bioinert,” as used herein, can refer to a material that does not elicitan immune response from a human or animal when it is disposed within anin-vivo biological environment. For example, a biological markerindicative of an immune response remains substantially constant (plus orminus 5% of a baseline value) when a human or animal is exposed to or incontact with the bioinert material. In some embodiments herein, bioinertdevices are provided.

After exposure to light, the photo-curable material may become cured,and may at that point include crosslinked polymers. In some embodiments,the crosslinked polymers are characterized by a tensile stress-straincurve that displays a yield point after which the test specimencontinues to elongate, but there is no increase in load. Such yieldpoint behavior typically occurs “near” the glass transition temperature,where the material is between the glassy and rubbery regimes and may becharacterized as having viscoelastic behavior. In some embodiments,viscoelastic behavior is observed in the temperature range 20° C. to 40°C. The yield stress is determined at the yield point. In someembodiments, the modulus is determined from the initial slope of thestress-strain curve or as the secant modulus at 1% strain (e.g. whenthere is no linear portion of the stress-strain curve). The elongationat yield is determined from the strain at the yield point. When theyield point occurs at a maximum in the stress, the ultimate tensilestrength is less than the yield strength. For a tensile test specimen,the strain is defined by In (I/I₀), which may be approximated by(I−I₀)/I₀ at small strains (e.g. less than approximately 10%) and theelongation is I/I₀, where I is the gauge length after some deformationhas occurred and I₀ is the initial gauge length. The mechanicalproperties can depend on the temperature at which they are measured. Thetest temperature may be below the expected use temperature for a dentalappliance such as 35° C. to 40° C.

In some embodiments, the one or more of the materials has a glasstransition temperature (Tg) of over 70° C. or of over 100° C., whichprevents the polymers from softening, thus contributing to thedimensional stability and accuracy of shape of the cured products. Thepresence of oligomeric, i.e. relatively low-molecular-weight of about0.4 to 5 kDa, glass transition temperature modifier(s) may provide forthe relatively high glass transition temperature.

The one or more materials may additionally have a decreased rigidity andincreased toughness and flexibility, as expressed by a tensile modulusof about 800-1,000 MPa, a tensile strength at yield of about 25-40 MPa,an elongation at break of about 20-30%, a stress relaxation of about20-35% of the initial load, and/or a stress relaxation of 2-3 MPa after2 hours, when examined under test conditions of a temperature of 37±2°C. at 100% relative humidity or a temperature of 37±2° C. in water, i.e.at about body temperature. In some embodiments, the one or morematerials has one or more of the following properties: a tensile modulusgreater than or equal to 800 MPa, an elongation at break greater than orequal to 20%, a stress remaining after 2 h of greater than or equal to20% of the initial load, and/or a glass transition temperature ofgreater than or equal to 80° C. In further embodiments, the material(e.g., crosslinked polymer) has one or more of the following properties:a tensile modulus greater than or equal to 1,000 MPa, an elongation atbreak greater than or equal to 30%, a stress remaining after 2 h ofgreater than or equal to 35% of the initial load, and/or a glasstransition temperature of greater than or equal to 90° C. In someembodiments, the material has a glass transition temperature (Tg) ofabout 100 to about 120° C. In some embodiments, the material has astorage moduli at 20° C. of about 2000 MPa to about 2800 GPa. In someembodiments, the material reaches a storage moduli of 1000 MPa at about60-120° C. At least some of the above mechanical properties may beenabled by the presence of polymeric, i.e. high-molecular-weight (>5kDa), toughness modifier(s) in embodiments.

Other materials (resins, formulations, monomers, polymers, oligomers,etc.) and/or methods that can be used by the techniques described hereininclude the subject matter of U.S. Pat. Pub. No. 2017/0007362, to YanCHEN et al., entitled, “Dental Materials Using Thermoset Polymers;”International Patent Application Number PCT/US2019/030683 to ALIGNTECHNOLOGY, INC., entitled “Curable Composition for Use in a HighTemperature Lithography-Based Photopolymerization Process and Method ofProducing Crosslinked Polymers Therefrom; and International PatentApplication Number PCT/US2019/030687 to ALIGN TECHNOLOGY, INC.,entitled, “Polymerizable Monomers and Method of Polymerizing the Same.”The subject matter of these applications and all other patents andpatent publications listed in this disclosure are hereby incorporated byreference as if set forth fully herein.

The hybrid 3D printer 200 may additionally include a light source 230that generates a light beam 235 that is precisely directed onto portionsof the 3D object 222. Some portions of the object 222 are exposed to thelight beam 235, and become cured portions 225. Other portions of theobject 222 are not exposed to the light beam 235, and remain uncuredportions 230. As shown, the uncured portions 230 may have a first shapeand the cured portions 225 may have a second shape that is encapsulatedwithin the first shape.

The hybrid 3D printer 200 may additionally include a controller (notshown) that controls the position and movements of the dispenser 215,the platform 205 and/or the light source 230. The controller may sendinstructions to stepper motors for the dispenser 215 and/or platform 205according to a digital file such as a digital file having astereolithography (STL) file format, an OBJ file format, an Filmbox(FBX) file format, a COLLADA file format, a 3DS file format, an InitialGraphics Exchange Specification (IGES) file format, a STEP file format,or other 3D file format to achieve computer aided manufacturing (CAM).Through the coordinated movement of the platform 205 and/or dispenser215, a 3D object 222 may be created by printing one layer of the 3Dobject 222 at a time.

In some embodiments, the light source 230 is a laser such as anultraviolet (UV) laser. In various embodiments, the light source 230 hasa fixed position, and directs the light beam 235 onto a scanning mirror240 (e.g., such as an x-y scanning mirror). The scanning mirror 240 maythen be controlled by the controller to direct the light beam to atarget location in the xy plane. The scanning mirror 240 moves the lightbeam in a pattern across the uppermost layer of the object 222 accordingto the digital file to cure some portions of the uppermost layer andoptionally one or more lower layers of the object 222. In an alternativeembodiment, the light source 230 itself may be movable (e.g., rotatable)to direct the light beam to target locations within the interior volume245. In another embodiment, the light source 230 may be attached to thedispenser 215 (e.g., to a nozzle of the dispenser). For example, theylight source 230 may have a fixed position that directs the light beamto a fixed point below the nozzle of the dispenser 215. Alternatively,the light source 230 may be attached to the dispenser 215, but may bemovable (e.g., rotatable) to adjust where the light beam is directed.The laser may scan the uppermost layer of the object 222 according tothe digital file to cure portions of the object in embodiments.

In some embodiments, the light source 230 is a high-definition DLPprojector (e.g., which may emit UV light beams). The DLP projector canemit light onto multiple locations of the platform 205 and/or object 222simultaneously. The DLP projector may divide the area under the DLPprojector into a grid of pixels, and the DLP projector may control foreach pixel whether that pixel is exposed to light. Additionally, eachpixel of the projector can be output in a spectrum from white to gray toblack. This enables each pixel location to be cured to a differentdepth. Accordingly, the object 222 may be divided into voxels, and theamount of light exposure to each voxel may be controlled.

Though only a single light source 230 is shown, in embodiments the 3Dprinter 200 may include multiple light sources (e.g., two or more lightsources), each of which may generate light beams that may be directedindependently and which may operate in parallel to speed up the curingof the photo-curable material deposited onto the platform 205. When morethan one light source is used, it may be different types of lightsources, such as Laser, DLP of a different wavelength, etc.

In some embodiments, the light beam 235 is directed to the uppermostlayer of the object 222 while the deposited photo-curable material atthe uppermost layer is still hot (e.g., at around 90-120° C.).Alternatively, the uppermost layer of the object 222 may be allowed tocool before the light beam 235 is directed to the uppermost layer. Insome embodiments, the deposited material will solidify quickly afterbeing deposited. This allows the object to be built without the use ofany support structures (or with minimal use of support structures) sincethe photo-cured portion 225 of the object 222 is encapsulated within andsupported by the uncured portion 230, which may be frozen (e.g., solid)when it cools.

As shown, the light source 230 is mounted above the dispenser 215.However, the light source 230 may be below the dispenser 215 or coplanarwith the dispenser 215 in embodiments. In an example, the light source230 and the dispenser 215 may both be mounted to a mechanical stage.

In some embodiments, the 3D printer 200 further includes one or moreheaters (not shown) that may maintain a temperature of the depositedmaterial (e.g., object 222) at a level that is suitable for curing(e.g., photo-curing) of the material. The heater(s) may be mounted tothe platform 205, to the bottom 260, to the sides 255, or elsewhere onthe 3D printer 200 at one or more mixed positions. Alternatively, oradditionally, one or more heaters may be mounted to the dispenser 215(or to a mechanical stage to which the dispenser 215 may be mounted) todirect heat, for example, toward the output of the nozzle.Alternatively, or additionally, one or more heaters may be mounted to aguideway and may be independently movable to heat target portions of theobject 222 to coincide with the light beam 235 being directed to thetarget portions. Accordingly, the heater may follow or precede the lightbeam 235 to control the local temperature of portions of the object 222during the curing process. This may help to control warpage and/orshrinkage of the object 222 during curing, for example.

In some embodiments, one or more chillers may be included in the 3Dprinter 200 in addition to, or instead of, one or more heaters. Thechiller(s) may be mounted, for example, to the platform 205 and/orelsewhere in the 3D printer 200. The chillers may include one or moreconduits through which chilled fluid is flowed, for example.

In some embodiments, the 3D printer 200 further includes a heater (notshown) that may heat the interior volume 245 to a target temperature(e.g., about 60-130° C., or 90-120° C., or higher) that melts orliquefies the uncured portions 230 of the object 222 after the objecthas been completed. This may cause the high viscosity uncured material230 to melt away and separate from the cured portion 225 of the object.Alternatively, once the object is complete, the object 222 may beremoved from the 3D printer 200 and placed in an oven, which may heatthe object 222 to the target temperature to melt the uncured portion 230and separate the uncured portion 230 from the cured portion 225.Additionally or alternatively, the object may undergo solvent washingsuch as isopropanol and/or other solvents that are able to dissolveuncured material but not substantially affect cured material.

FIG. 3A illustrates a top-down view of a cross section of a printedlayer 300 that has been printed using a hybrid 3D printer, in accordancewith some embodiments. In some embodiments, the printed layer 300 isprinted by hybrid 3D printer 200 of FIG. 2 . As shown, the printed layer300 includes an uncured portion 305 that has been deposited through anozzle 320 having a particular diameter. The diameter of the nozzle 320(and thus the minimum line width of the uncured portion 305 of theprinted layer 300) may be about 250-800 microns in embodiments. Infurther embodiments, the diameter of the nozzle 320 (and thus theminimum line width of the uncured portion 305 of the printed layer 300)may be about 100-800 microns. The light beam 315 that is directed to theprinted layer 300 may have a beam diameter of about 20-200 microns(e.g., about 100-200 microns) in embodiments. Accordingly, the curedportion 310 of the printed layer 300 may have a minimum diameter ofabout 20-200 microns (e.g., about 100-200) microns in embodiments. Sincethe minimum line width of the cured portion 310 may be much smaller thanthe minimum line width of the uncured portion 305, the level of detailthat is attainable using the hybrid 3D printing technique describedherein is much greater than the level of detail typically achievableusing FDM. Additionally, the level of accuracy of the light beam 315 isgenerally much higher than the level of accuracy achievable by thedispenser. Accordingly, the hybrid 3D printing technique describedherein also achieves a much greater level of accuracy than what isachievable using FDM.

FIG. 3B illustrates another top-down view of a cross section of aprinted layer 350 that has been printed using a hybrid 3D printer, inaccordance with some embodiments. In some embodiments, the printed layer350 is printed by hybrid 3D printer 200 of FIG. 2 . As shown, theprinted layer 350 includes an uncured portion 355 that has a firstminimum line width 365 and a cured portion 360 that has a lower secondminimum line width 370. The cured portion 360 of the printed object 350may have been exposed to a light beam output by a laser and/or a lightbeam output by a DLP projector. In the case of the DLP projector, theminimum line width may correspond to a pixel size of the DLP projector.

FIG. 4 illustrates a flow diagram for a method 400 of performing 3Dprinting, in accordance with some embodiments. One or more operations ofmethod 400 are performed by a hybrid 3D printer such as 3D printer 200of FIG. 2 in accordance with instructions from a digital file. Theinstructions may be sent by processing logic of a computing deviceconnected to the hybrid 3D printer. For example, computing device 500 ofFIG. 5 may execute a CAM module 550 that processes a digital file 552and provides instructions to the hybrid 3D printer based on theprocessing of the digital file 552. Alternatively, the instructions maybe generated by a controller of the 3D printer based on a digital file.

At block 402 of method 400, a 3D printer heats a photo-curable materialto a processing temperature. The processing temperature may be atemperature of above 60° C. in some embodiments. In a furtherembodiment, the processing temperature may be about 60-130° C. In afurther embodiment, the processing temperature may be about 90-120° C.In other embodiments, the processing temperature is 20-30° C. In stillother embodiments, the processing temperature is less than 20° C. orgreater than 130° C.

At block 405, the 3D printer moves a nozzle (e.g., a dispenser thatincludes the nozzle) according to a digital file. The 3D printer mayreceive instructions from a CAM module executing on a computing devicein some embodiments. In some embodiments, the digital file is loadedinto a controller of the 3D printer, and the 3D printer determines adeposition sequence (e.g., a sequence of positions of the nozzle and/orof heights of a platform) to achieve a printed object. At block 410, the3D printer extrudes the heated photo-curable material from the nozzle toform a layer of an object (a 3D printed part). The 3D printer may movethe nozzle while the photo-curable material is extruded from the nozzle.

At block 415, the 3D printer directs a light beam onto the layer of theobject according to the digital file or according to an additionaldigital file. For example, a first digital file may be used to determinewhere to extrude the one or more materials, and a second digital filemay be used to determine where to direct the one or more light sources.Alternatively, the same digital file may be used to determine where toextrude the material and where to direct the light beam. In someembodiments, the light beam is directed to a portion of the layer thathas been deposited while that portion of the layer is still heated(e.g., while the portion is still at or near the elevated processingtemperature). Alternatively, or additionally, the light beam may bedirected to the portion of the layer after the portion of the layer hascooled. The extruded photo-curable material may cool down rapidly afterdeposition, and may solidify in some embodiments. Accordingly, theuncured portions of the extruded material may encapsulate and supportthe cured portions of the material. Notably, the minimum line width ofthe cured portion of the object may be significantly thinner than theminimum line width of the uncured portion of the object.

At block 420, processing logic of the 3D printer (or of a computingdevice in communication with the 3D printer) may determine whether thecurrent layer is complete. If the current layer is not complete, themethod returns to block 405, the nozzle is moved (e.g., in the xyplane), and additional material is deposited at the layer. If thecurrent layer is complete, the method continues to block 425.

The light beam used to cure a top layer of the printed object may have asufficient power to penetrate below the top layer. For example, thelight beam may penetrate to a depth of 2 or more layers. The cure depthmay be greater than a layer thickness to ensure that touching layers arebonded together by the photopolymerization process. Accordingly,processing logic (e.g., of a controller of the 3D controller or of acomputing device coupled to the 3D printer) may compensate for the curedepth to ensure that only portions of the object that are meant to becured are in fact cured. For example, if a third layer is to be cured ata location, but a second layer below the third layer is not to be curedat the location, then the location may not be cured until the fourthlayer has been deposited. Once the fourth layer is deposited at thelocation (e.g., xy coordinate), then the location may be cured, curingboth the fourth layer and the third layer at the location, and leavingthe first and second layers uncured at the location. Or, as mentionedprevious, a grey scale light intensity can be used to control the depthof penetration into the layers.

At block 425, the processing logic of the 3D printer (or of a computingdevice in communication with the 3D printer) may determine whether the3D printed object is complete. If the 3D printed object is not complete,the method proceeds to block 430, and the 3D printer moves the nozzleand/or a platform supporting the object in the z direction to advance tothe next layer. The method then returns to block 405, and additionalmaterial is deposited to form the next layer. If the 3D printed objectis complete at block 425, the method continues to block 435.

At block 435, the 3D printed object is heated (e.g., to the processingtemperature or to another temperature that may be above the processingtemperature). The heating of the printed object may cause the uncuredportions of the printed object to melt and flow away from the curedportion of the printed object. Additionally, heating the printed objectmay further cure the cured portion of the printed object in someembodiments. At block 440, the uncured portions of the object may beseparated from the cured portions of the object. This separation mayoccur merely by the heating of the object (at block 435), or byperforming some additional process while the object is heated, such asrinsing with a heated fluid (e.g., by spraying a heated fluid at theobject), by agitating the object, by spinning the object, and so on.

The printed object may have relatively low level (rough) details priorto separating the cured portion of the object from the uncured portionof the object due to the diameter of the nozzle used to deposit thephoto-curable material and form the object. However, after separatingthe uncured portion from the cured portion, the resultant object mayhave high level (fine) details due to the small beam diameter of thelight used to cure the cured portion of the object. Thus, the resultant3D printed object may have a level of accuracy and detail that is on parwith that of objects printed using SLA and DLP 3D printing techniques.

It is understood that multiple dispensing heads can be used and each maydispense one or more materials. Some of the dispensed materials may bestandard FDM materials that do not require photo-curing or other curingmechanisms. It is also understood that while this hybrid printer isdescribed using high viscosity resins and materials, it can also be usedwith low viscosity materials such as is standard for DLP and SLAprinters. Also, it is understood that other curing mechanisms such astwo part mixing of materials during dispensing is also possible (such asis possible with a static mixing head added to two (or more) dispensingheads) to create a mixed material that reacts either right away and/orlater and/or with heating and/or with light.

Since the embodiments described herein are able to dispense multiplematerials, some of those materials may comprise drugs such as hormones,analgesics, antimicrobial compounds, dyes, pH sensitive materials,pigments, gels, fragrances, flavors, catalysts, initiators, inhibitors,light blockers, UV blockers, etc. These materials may be dispensed ontheir own or mixed with resins or thermoplastics or solvents. Obviously,mixtures of materials are included.

It is also understood that the use of supports is sometimes needed ordesired. With some embodiments, the ability to print an object withmultiple materials also allows for making the supports out of adifferent material than the printed object. The support material may ormay not be a photo-cured material. The support material may be designedto dissolve in solvents such as water or isopropyl alcohol or ethanol(or other solvents). It may be a wax material or other material thateasily melts away during heating.

Various embodiments also provide the ability to incorporate pick andplace technology into the printing method. For example, a robotic armcan pick up a self-contained electronic device (such as an electroniccompliance indicator and place it into a specified layer of the print.Printing can continue and may fully encase the electronic device incured material. Other objects can also be placed into any given layer ofthe print to fulfill other functions such as added structural supportfor the printed object or imbedded sensors.

In some embodiments, an optical sensing system is used to locate thesurface of the layer to determine the exact height of the layer. Thiscan facilitate control of the focal point of light used to cure thephoto-curable material. It can also be used to spatially locate objectsduring print (such as objects that have been added via a robotic arm).It can also be used to verify that cure has occurred such as if theoptical system uses fluorescence to determine the extent of cure. Otheroptical sensors can be incorporated into the printer such as FTIR, IR,NIR, Raman, to help determine the extent of cure or the location oramount of dispensed materials.

Method 400 may be performed to manufacture orthodontic aligners andother dental appliances to be worn over a patient's dental arches. Theshape of each aligner is unique and customized for a particular patientand a particular treatment stage. Each aligner may be manufacturedaccording to a unique digital file that corresponds to an aligner thatwill fit over an upper or lower dental arch of a particular patient at aparticular treatment stage. Each aligner will apply forces to thepatient's teeth at a particular stage of the orthodontic treatment. Thealigners each have teeth-receiving cavities that receive and resilientlyreposition the teeth in accordance with a particular treatment stage.Teeth may be repositioned by the aligners by, for example, moving one ormore teeth vertically, rotating one or more teeth, moving one or moreteeth in a transverse direction relative to the dental arch, and/ormoving one or more teeth in an anterior-posterior direction relative tothe dental arch. Each aligner may additionally include shapes thataccommodate features attached to a patient's dentition that facilitatetooth repositioning and/or rotation.

FIG. 5 illustrates a diagrammatic representation of a machine in theexample form of a computing device 500 within which a set ofinstructions, for causing the machine to perform any one or more of themethodologies discussed with reference to method 400. In alternativeembodiments, the machine may be connected (e.g., networked) to othermachines in a Local Area Network (LAN), an intranet, an extranet, or theInternet. For example, the machine may be networked to a rapidprototyping apparatus such as a 3D printer such as 3D printer 200 ofFIG. 2 . The machine may operate in the capacity of a server or a clientmachine in a client-server network environment, or as a peer machine ina peer-to-peer (or distributed) network environment. The machine may bea personal computer (PC), a tablet computer, a set-top box (STB), aPersonal Digital Assistant (PDA), a cellular telephone, a web appliance,a server, a network router, switch or bridge, or any machine capable ofexecuting a set of instructions (sequential or otherwise) that specifyactions to be taken by that machine. Further, while only a singlemachine is illustrated, the term “machine” shall also be taken toinclude any collection of machines (e.g., computers) that individuallyor jointly execute a set (or multiple sets) of instructions to performany one or more of the methodologies discussed herein.

The example computing device 500 includes a processing device 502, amain memory 504 (e.g., read-only memory (ROM), flash memory, dynamicrandom access memory (DRAM) such as synchronous DRAM (SDRAM), etc.), astatic memory 506 (e.g., flash memory, static random access memory(SRAM), etc.), and a secondary memory (e.g., a data storage device 528),which communicate with each other via a bus 508.

Processing device 502 represents one or more general-purpose processorssuch as a microprocessor, central processing unit, or the like. Moreparticularly, the processing device 502 may be a complex instruction setcomputing (CISC) microprocessor, reduced instruction set computing(RISC) microprocessor, very long instruction word (VLIW) microprocessor,processor implementing other instruction sets, or processorsimplementing a combination of instruction sets. Processing device 502may also be one or more special-purpose processing devices such as anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), a digital signal processor (DSP), network processor,or the like. Processing device 502 is configured to execute theprocessing logic (instructions 526) for performing operations and stepsdiscussed herein.

The computing device 500 may further include a network interface device522 for communicating with a network 564. The computing device 500 alsomay include a video display unit 510 (e.g., a liquid crystal display(LCD) or a cathode ray tube (CRT)), an alphanumeric input device 512(e.g., a keyboard), a cursor control device 514 (e.g., a mouse), and asignal generation device 520 (e.g., a speaker).

The data storage device 528 may include a machine-readable storagemedium (or more specifically a non-transitory computer-readable storagemedium) 524 on which is stored one or more sets of instructions 526embodying any one or more of the methodologies or functions describedherein. A non-transitory storage medium refers to a storage medium otherthan a carrier wave or other propagating signal. The instructions 526may also reside, completely or at least partially, within the mainmemory 504 and/or within the processing device 502 during executionthereof by the computer device 500, the main memory 504 and theprocessing device 502 also constituting computer-readable storage media.

The computer-readable storage medium 524 may also be used to store oneor more virtual 3D models in the form of digital files 552 and/or acomputer aided manufacturing (CAM) module 550. The CAM module 550 mayprocess the digital file 552 to determine the sequence of positions of adispenser (e.g., an extruder) and/or a platform that will result in 3Dprinted object defined by the digital file 552. The CAM module 550 maysend instructions to a 3D printer to cause the 3D printer to perform oneor more of the operations of method 400. While the computer-readablestorage medium 524 is shown in an example embodiment to be a singlemedium, the term “computer-readable storage medium” should be taken toinclude a single medium or multiple media (e.g., a centralized ordistributed database, and/or associated caches and servers) that storethe one or more sets of instructions. The term “computer-readablestorage medium” shall also be taken to include any medium that iscapable of storing or encoding a set of instructions for execution bythe machine and that cause the machine to perform any one or more of themethodologies described herein. The term “computer-readable storagemedium” shall accordingly be taken to include, but not be limited to,solid-state memories, and optical and magnetic media.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent upon reading and understanding the above description. Althoughembodiments have been described with reference to specific examples, itwill be recognized that the invention is not limited to the embodimentsdescribed, but can be practiced with modification and alteration withinthe spirit and scope of the appended claims. Accordingly, thespecification and drawings are to be regarded in an illustrative senserather than a restrictive sense. The scope of the invention should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

Example experiments were performed, as set forth below.

In a first example, material A, material B, and material C were placedinto 1 mL syringes with a 22 gauge flat top needle. Material A was a hotmelt adhesive. Material B was TCDDA with 1 wt % TPO-L. Material C wast-butyl acrylate with 1 wt % TPO-L. In the experiment, material A wasextruded onto a glass slide in the form of a circle. Material B was thendispensed to fill the inside of the circle. A dog bone pattern wasprojected onto the liquid inside the circle, creating a dog bone printto form. The print was fully inside the outer circle. Then material Awas dispensed on top of the previous circle to increase the height ofthe vat and then cured. Then material C was dispensed into the circle tofill the reservoir with material C. The dog bone pattern was exposedonto the liquid resin in the same location as the previous projection.The material C cured in the shape of the dog bone. The process wasrepeated 4 more times to form a material with 5 layers of material B and5 layers of material C in alternating layers in the shape of the dogbone. The composite nature of the dog bone was confirmed using FTIR andRaman spectroscopy to identify each layer of the composite.

In another experiment, the vat was formed layer by layer as demonstratedbefore, but materials B and C were dispensed side by side in each layersuch that when the exposure was made, the left half of the dog bone wasmaterial B and the right half of the dog bone was material C. Theinterface between the two materials underwent some mixing before theexposure occurred and so the interface represents a new material whichis a mixture of materials B & C.

What is claimed is:
 1. A method of three-dimensionally (3D) printing anorthodontic aligner, comprising: extruding one or more photo-curablematerials from a nozzle to form a first layer of the one or moreextruded photo-curable materials according to one or more digital files,wherein the first layer of the one or more extruded photo-curablematerials has a first shape specified by the one or more digital files,wherein the first shape of the one or more extruded photo-curablematerials corresponds to a first minimum line width that is based on,and narrower than, a diameter of the nozzle; and directing a light beamonto the first layer of the one or more extruded photo-curable materialsaccording to the one or more digital files to cure a portion of thefirst layer of the one or more extruded photo-curable materials tocreate a first cured layer of the one or more photo-curable materials,wherein the first cured layer of the one or more photo-curable materialscorresponds to a second shape of a first layer of a 3D printedorthodontic aligner specified by the one or more digital files, whereinthe light beam has a beam diameter that is smaller than the diameter ofthe nozzle, and wherein the second shape has a second minimum line widththat is smaller than the first minimum line width.
 2. The method ofclaim 1, further comprising: extruding the one or more photo-curablematerials from the nozzle to form a second layer of the one or moreextruded photo-curable materials over the first layer of the one or moreextruded photo-curable materials according to the one or more digitalfiles, wherein the second layer of the one or more extrudedphoto-curable materials has a third shape specified by the one or moredigital files; and directing the light beam onto the second layer of theone or more extruded photo-curable materials according to the one ormore digital files to cure a portion of the second layer of the one ormore extruded photo-curable materials to create a second cured layer ofthe one or more photo-curable materials, wherein the second cured layerof the one or more photo-curable materials corresponds to a fourth shapeof a second layer of the 3D printed orthodontic aligner, wherein thelight beam penetrates the second layer of the one or more extrudedphoto-curable materials and at least a portion of the first layer of theone or more extruded photo-curable materials to bond the second curedlayer of the one or more photo-curable materials to the first curedlayer of the one or more photo-curable materials.
 3. The method of claim1, wherein the light beam cures the portion of the first layer before anentirety of the first shape of the first layer is formed, and whereinthe one or more photo-curable materials are bioinert and biocompatibleafter being cured.
 4. The method of claim 1, wherein the first layer ofthe one or more extruded photo-curable materials is an intermediatelayer of the one or more extruded photo-curable materials, the methodfurther comprising: heating the first layer of the one or more extrudedphoto-curable materials; and removing uncured portions of the firstlayer of the one or more extruded photo-curable materials to separatethe uncured portions of the first layer from the first cured layer. 5.The method of claim 1, further comprising: repositioning at least one ofthe nozzle or a supporting platform while extruding the one or morephoto-curable materials to form the first shape; and repositioning atleast one of the light beam or the supporting platform after a portionof the first layer has been extruded to form the second shape within thefirst shape.
 6. The method of claim 1, wherein the light beam is anultraviolet (UV) light beam, the method further comprising: generatingthe light beam using at least one of a UV laser or a UV digital lightprocessing (DLP) projector.
 7. The method of claim 1, wherein at leastone photo-curable material of the one or more photo-curable materialscomprises long chain monomers, has a first viscosity of less than 2Pascal-seconds (Pa-s) while it is heated to a temperature of about60-130 degrees Celsius (° C.) and a second viscosity of greater than 10Pa-s at room temperature.
 8. The method of claim 1, wherein the firstminimum line width is about 100-800 microns and the second minimum linewidth is about 20-200 microns.
 9. The method of claim 1, wherein the 3Dprinted orthodontic aligner comprises at least one of a tensile modulusof about 800-1000 MPa, a tensile strength of about 25-40 MPa, or anelongation at break of about 20-30% at a temperature of about 37+/−2° C.10. The method of claim 1, wherein the light beam is directed onto theportion of the first layer of the one or more extruded photo-curablematerials to cure the portion of the first layer of one or more extrudedphoto-curable materials before the portion of the first layer of one ormore extruded photo-curable materials has cooled.
 11. The method ofclaim 1, wherein the light beam follows a same path as the nozzle. 12.The method of claim 1, wherein the light beam is directed onto theportion of the first layer of the one or more extruded photo-curablematerials while the nozzle continues to extrude the one or morephoto-curable materials to form a remainder of the first layer of theone or more extruded photo-curable materials.
 13. The method of claim 1,whereon the one or more photo-curable materials comprise a firstphoto-curable material and a second photo-curable material, whereinextruded first photo-curable material has a first line width that isdifferent from a second line width of extruded second photo-curablematerial.
 14. The method of claim 1, whereon the one or morephoto-curable materials comprise a first photo-curable material and asecond photo-curable material that are extruded from the nozzle at asame time.
 15. The method of claim 14, wherein the extruded firstphoto-curable material has a first line width that is less than a secondline width of extruded second photo-curable material.
 16. The method ofclaim 14, wherein the extruded first photo-curable material has a firstline width, wherein the second photo-curable material has a second linewidth, and wherein at least one of the first line width or the secondline width is less than the diameter of the nozzle.
 17. The method ofclaim 1, further comprising: applying one or more stimuli to cause theone or more photo-curable materials to have one or more rheologicalproperties.
 18. The method of claim 17, wherein applying the one or morestimuli comprises at least one of heating the one or more photo-curablematerials or introducing a reactive diluent to the one or morephoto-curable materials.
 19. A 3D printer, comprising: a platform; adispenser comprising a nozzle to extrude one or more photo-curablematerials onto the platform to form a first layer of the one or moreextruded photo-curable materials according to one or more digital files,wherein the first layer of the one or more extruded photo-curablematerials is to have a first shape specified by the one or more digitalfiles, wherein the nozzle is configured such that the first shape of theone or more extruded photo-curable materials corresponds to a firstminimum line width that is based on, and narrower than, a diameter ofthe nozzle; and a light source to emit a light beam that is directedonto the first layer of the one or more extruded photo-curable materialsaccording to the one or more digital files to cure a portion of thefirst layer of the one or more extruded photo-curable materials tocreate a first cured layer of the one or more photo-curable materials,wherein the first cured layer of the one or more photo-curable materialscorresponds to a second shape of a first layer of a 3D printedorthodontic aligner specified by the one or more digital files, whereinthe light beam has a beam diameter that is smaller than the diameter ofthe nozzle, and wherein the second shape has a second minimum line widththat is smaller than the first minimum line width.
 20. The 3D printer ofclaim 19, wherein the light source is attached to the dispenser and isconfigured to direct the light beam to a fixed point below the nozzle ofthe dispenser.
 21. The 3D printer of claim 19, wherein the light sourceis attached to the dispenser and is movable to adjust a direction of thelight beam relative to the nozzle of the dispenser.
 22. The 3D printerof claim 19, wherein the first layer of the one or more extrudedphoto-curable materials is an intermediate layer of the one or moreextruded photo-curable materials, the 3D printer further comprising: aheater to heat the first layer of the one or more extruded photo-curablematerials, wherein uncured portions of the first layer of the one ormore extruded photo-curable materials are removed while heated toseparate the uncured portions of the first layer from the first curedlayer.
 23. The 3D printer of claim 19, further comprising: a controllerto: reposition at least one of the nozzle or the platform while the oneor more photo-curable materials are extruded to form the first shape;and reposition at least one of the light beam or the platform after aportion of the first layer has been extruded to form the second shapewithin the first shape.
 24. The 3D printer of claim 19, wherein thelight beam is an ultraviolet (UV) light beam, and wherein the lightsource comprises at least one of a UV laser or a UV digital lightprocessing (DLP) projector.
 25. The 3D printer of claim 19, furthercomprising: a controller to cause the light beam to cure the portion ofthe first layer before an entirety of the first shape of the first layeris formed.
 26. The 3D printer of claim 19, further comprising: acontroller to cause the light beam to be directed onto the portion ofthe first layer of the one or more extruded photo-curable materials tocure the portion of the first layer of one or more extrudedphoto-curable materials before the portion of the first layer of one ormore extruded photo-curable materials has cooled.
 27. The 3D printer ofclaim 19, further comprising: a controller to cause the light beam tofollow a same path as the nozzle.
 28. The 3D printer of claim 19,whereon the one or more photo-curable materials comprise a firstphoto-curable material and a second photo-curable material, whereinextruded first photo-curable material has a first line width that isdifferent from a second line width of extruded second photo-curablematerial.
 29. The 3D printer of claim 19, whereon the one or morephoto-curable materials comprise a first photo-curable material and asecond photo-curable material that are extruded from the nozzle at asame time.
 30. The 3D printer of claim 29, wherein the nozzle is toextrude the first photo-curable material and the second photo-curablematerial such that the extruded first photo-curable material has a firstline width that is less than a second line width of extruded secondphoto-curable material.
 31. The 3D printer of claim 29, wherein thenozzle is to extrude the first photo-curable material and the secondphoto-curable material such that the extruded first photo-curablematerial has a first line width, the extruded second photo-curablematerial has a second line width, and at least one of the first linewidth or the second line width is less than the diameter of the nozzle.32. The 3D printer of claim 19, wherein the 3D printer is to apply oneor more stimuli to cause the one or more photo-curable materials to haveone or more rheological properties.
 33. The 3D printer of claim 32,wherein applying the one or more stimuli comprises at least one ofheating the one or more photo-curable materials, introducing a reactivediluent to the one or more photo-curable materials.